Insulated storage tanks for storing fluids at temperatures substantially independent of the ambient environment are widely used, particularly in northern climates. Generally, the construction of insulated tank structures for outdoor use involves the employment of heavy materials and complex support forms, thereby producing high labor and material costs which render such tanks expensive.
In the past, effective insulated storage tanks have been constructed from blocks of insulating material, such as Foamglas, a product of Pittsburgh Plate Glass Company. These blocks are set in place using hot pitch asphalt as the bonding agent between individual blocks. Subsequently, an asphalt coating combined with open mesh fiberglas cloth is used as an outer covering to protect the blocks from the elements and physical damage. Considerable labor costs are incurred in the construction of such tanks, for not only is asphalt difficult to work with, but the dangers involved in applying asphalt by hand to the blocks provides some hazard in the construction process.
Another known method for forming insulated tanks involves the use of cementious insulating block. In general, such block is an expanded shale or pumice which may weigh as much as 90 lbs. per cubic foot. This block, when treated on the exterior with a repellant material or a masonary type latex base paint, provides a tank with very dense walls and good thermal insulating characteristics, but construction costs are excessive due to the equipment and labor needed to handle such heavy block.
Ideally, lightweight foam insulation can be employed in the construction of large volume insulated tank structures, and methods for installing lightweight foam as an insulator are disclosed in U.S. Pat. Nos. 3,753,848 and 4,077,177. Unfortunately, where large volume, insulated tanks are required which have the capability of withstanding great internal hydrostatic pressure, it is necessary to provide the foam insulated tank with a strong, reinforcing core of cement or similar material. In the past, it has been necessary to first provide a structural form to support and reinforce the concrete core which is poured to form the basic tank structure. Then, the form is removed and insulating material is laid around the periphery of the concrete core. The necessity to deal with the tremendous weights involved in pouring a complete concrete tank and to provide the required form and support structures for this concrete has contributed to high labor and material costs for tank construction.